Garden with Insight v1.0 Help: Soil patch next day functions: for the top soil layer, calculate nitrate lost in runoff, lateral flow, and
percolation

Calculations of nitrate lost in water flow are different for the top soil layer than for the other soil layers. First, water running off the surface
of the soil takes some nitrate with it. Note that nitrate in rainfall and snowmelt was already added to the
soil without considering runoff, so we must adjust that here.
For the top soil layer, which is always 10 mm deep, nitrate lost in lateral
flow and runoff can be lumped together because the two water flows are virtually indistinguishable at
the soil surface.

All of the nitrate losses here use a common equation, which depends on the amount of nitrate in the layer,
the volume of water flowing through the layer, and the porosity of the
layer (higher porosity = more ease of flow). For nitrate lost in runoff
and lateral flow from the surface layer, the water volume is runoff plus lateral flow from the top layer. For
nitrate lost in percolation rom the top soil layer, percolated water is the
important water volume.